Formation Of Silver Nanoclusters Research Articles

Temperature‐Controlled Selective Formation of Silver Nanoclusters and Their Transformation to the Same Product

AbstractHerein, two atomically precise silver nanoclusters, Ag54 and Ag33, directed by inner anion templates (CrO42− and/or Cl−), are initially isolated as a mixed phase from identical reactants across a wide temperature range (20–80 °C). Interestingly, fine‐tuning the reaction temperature can realize pure phase synthesis of the two nanoclusters; that is, a metastable Ag54 is kinetically formed at a low temperature (20 °C), whereas such a system is steered towards a thermodynamically stable Ag33 at a relatively high temperature (80 °C). Electrospray ionization mass spectrometry illustrates that the stability of Ag33 is superior to that of Ag54, which is further supported by density functional theory calculations. Importantly, the difference in structural stability can influence the pathway of 1,4‐bis(pyrid‐4‐yl)benzene induced transformation reaction starting from Ag54 and Ag33. The former undergoes a dramatic breakage‐reorganization process to form an Ag31 dimer (Ag31), while the same product can be also achieved from the latter following a noninvasive ligand exchange process. Both the Ag54 and Ag33 have the potential for further remote laser ignition applications. This work not only demonstrates how temperature controls the isolation of a specific phase, but also sheds light on the structural transformation pathway of nanoclusters with different stability.

Silver ions-regulated two-stage photoluminescence transformations of glutathione-capped gold nanoclusters from near-infrared (NIR) to visible region: Anti-galvanic reaction and Ag deposition

In the present study, glutathione-capped gold nanoclusters (AuNCs@GSH) were prepared by an improved hydrothermal method, which showed near-infrared (NIR) emission centered at 805 nm. Besides, Ag+ can induce the NIR emission transformations in a two-stage mode under different concentration ranges of Ag+. At the first stage (0.50–15 μM), a new emission at 615 nm was generated while the original NIR emission was quenched upon Ag+ addition; at the second stage (15–120 μM), it shifted to 720 nm gradually along with more Ag+ addition, which realized precise regulation of the emission range of metal nanoclusters from red to NIR region. The in-depth mechanism investigation revealed the transformations in both stages originated from the anti-galvanic reaction (AGR) of AuNCs toward Ag+ and Ag deposition. In detail, the first stage was attributed to the formation of bimetallic gold and silver nanoclusters (Au-AgNCs); while the second stage ascribed to the Ag deposition-induced size growth and composition changes of Au-AgNCs. Therefore, the present study supplies a simple and rapid method for preparing NIR-emitted AuNCs and provides a facile approach to regulate the photoluminescence ranges based on the AGR and Ag deposition.

Dual‐Phosphorescent Heteroleptic Silver(I) Complex in Long‐Lasting Red Light‐Emitting Electrochemical Cells

AbstractThe design of red‐emitting silver(I) complexes and their implementation in thin‐film lighting are still challenging as (i) their high ligand‐field splitting energy leads to high‐energy emissions with a controversial mechanism (thermally activated delayed fluorescence vs fluorescence/phosphorescence), and (ii) their low electrochemical stability leads to the formation of silver nanoclusters, limiting device stability to a few seconds. Herein, a thoughtful complex design [Ag(xantphos)(deebq)]PF6 combining a large‐bite angle diphosphine ligand (xantphos), a rigid, sterically hindered, π‐extended biquinolin (deebq) is reported. In contrast to prior‐art, this complex possesses (i) efficient red‐emission (λem = 660 nm; photoluminescence quantum yield of 42%) assigned to a thermally equilibrated dual‐phosphorescent emission based on spectroscopic/theoretical studies and (ii) stable reduction behavior without forming silver nanoclusters. This results in the first red light‐emitting electrochemical cells featuring (i) improved stability of two orders of magnitude compared to prior‐art (from seconds to hours) at irradiances of 20 µW cm−2, and (ii) a new degradation mechanism exclusively related to p‐doping as confirmed by electrochemical impedance spectroscopy analysis. Indeed, a multi‐layered architecture to decouple hole injection/transport and exciton formation enables a further 2‐fold enhanced irradiance/stability. Overall, this work illustrates that deciphering the rules for silver(I) complex design for lighting is tricky, but worthwhile.

Sensitive Fluorescent Determination of Nucleic Acids by a Cytosine-Rich Loop and Silver Nanoclusters in the Hybridization Chain Reaction (HCR)

Deep understanding of the effect of DNA sequence and structure on the fluorescent properties of DNA-templated silver nanoclusters (DNA–Ag NCs) affords alternative strategies for developing and exploiting DNA biosensors. DNA secondary structures (e.g., DNA loop) are essential for generating highly emissive DNA–Ag NCs. In this study, a cytosine-rich DNA loop was used as a facile template for the formation of silver nanoclusters. The fluorescence of silver nanocluster encapsulated within a cytosine-rich DNA loop was turned on by switching the size of the loop from large to small. Target nucleic acid served as the trigger for the hybridization chain reaction of hairpin probe 1 (H1) containing an inactivated cytosine-rich DNA loop with a large size at the ends and hairpin probe 2 (H2). Long-nicked double helices were obtained coupled with the opening of the large-size cytosine-rich DNA loop in H1 and switching to an activated cytosine-rich DNA loop with a small size. As a result, an increase in the fluorescent signal was observed. A sensitive detection limit of 10 pM and a linear detection range from 10 pM to 400 nM were obtained for nucleic acid determination. This facile assay provides a new approach capable of switching the fluorescence emission of DNA–Ag NCs for nucleic acid biosensing.

Metallogels from Silver Nanoparticles and Peptide Nanofibers as Antimicrobial Surfaces

Peptide amphiphiles (PAs) are elusive candidates to construct soft materials possessing various functionalities, including potent antimicrobial activity. It is imperative to look for a broad-spectrum antibiotic against which the genesis of drug resistance is difficult. Herein, a histidine-based PA is found to form a transparent metallohydrogel when AgNO3 is added to a hot solution of the PA in 2:1 (PA/AgNO3) molar ratio. Exposure to 365 nm UV lamp results in blue light-emitting silver nanocluster (NC) formation inside the hydrogel matrix. Interestingly, when the metallohydrogel is turned in solution through sheer thinning and rested for 12–14 h in ambient light, the gel reforms along with the formation of non-fluorescent silver nanoparticles (NPs). Thus, two different nanomaterials can be synthesized separately inside the gel matrix with modulation of the conditions. As the NC and NP formation takes place, ordered growth of these nanomaterials can be observed along the nanofibrous hydrogel network. Rheological measurements show enhancement of storage modulus in NC- and NP-containing hybrid hydrogels. This new nanohybrid system comprising peptide gel-based nanofibers and silver NC/NPs has potential applications against Gram-positive and Gram-negative bacteria. Furthermore, the plausible mechanism of the antimicrobial effects has been thoroughly investigated. The elevated levels of reactive oxygen species (ROS) found in the bacteria in the presence of the hybrid hydrogels establish that intra-cellular ROS generated in the cytosol of the bacteria is responsible for the death of bacteria. The current work indicates the hybrid hydrogel’s utility as a potent antimicrobial agent.

Heat, pH, and salt: synthesis strategies to favor formation of near-infrared emissive DNA-stabilized silver nanoclusters.

We present chemical synthesis strategies for DNA-stabilized silver nanoclusters (AgN-DNAs) with near-infrared (NIR) emission in the biological tissue transparency windows. Elevated temperatures can significantly increase chemical yield of near-infrared nanoclusters. In most cases, basic pH favors near-infrared nanoclusters while micromolar amounts of NaCl inhibit their formation.

Protein cysteine S-glycosylation: oxidative hydrolysis of protein S-glycosidic bonds in aqueous alkaline environments

Some glycoproteins contain carbohydrates S-linked to cysteine (Cys) residues. However, relatively few S-glycosylated proteins have been detected, due to the lack of an effective research methodology. This work outlines a general concept for the detection of S-glycosylation sites in proteins. The approach was verified by exploratory experiments on a model mixture of β-S-glucosylated polypeptides obtained by the chemical transformation of lysozyme P00698. The model underwent two processes: (1) oxidative hydrolysis of S-glycosidic bonds under alkaline conditions to expose the thiol group of Cys residues; (2) thiol S-alkylation leading to thiol S-adduct formation at the former S-glycosylation sites. Oxidative hydrolysis was conducted in aqueous urea, dimethyl sulfoxide, or trifluoroethanol, with silver nitrate as the reaction promoter, in the presence of triethylamine and/or pyridine. The concurrent formation of stable protein silver thiolates, gluconic acid, and silver nanoclusters was observed. The essential de-metalation of protein silver thiolates using dithiothreitol preceded the S-labeling of Cys residues with 4-vinyl pyridine or a fluorescent reagent. The S-labeled model was sequenced by tandem mass spectrometry to obtain data on the modifications and their distribution over the protein chains. This enabled the efficiency of both S-glycosidic bonds hydrolysis and S-glycosylation site labeling to be evaluated. Suggestions are also given for testing this novel strategy on real proteomic samples.

Effect of a stabilizer on the structure, synthesis, and tribological properties of silver nanoparticles

The structure and properties of nanoparticles are greatly influenced by the synthesis method and the stabilizer used in their preparation. The paper presents the results of the effect of various stabilizers (gelatin, sodium citrate, sodium borohydride) on the structure, synthesis, and tribotechnical properties of silver nanoparticles. The mechanism of the formation and growth of silver nanoclusters was investigated using quantum-chemical calculations with full optimization of all parameters using the density functional theory (DFT) PBEPBE/Lanl2DZ method. It is shown that the use of organic stabilizers (for example, gelatin) leads to an increase in the stability of stabilized silver clusters. Such systems have greater conformational flexibility and a large number of molecular donor oxygen centres in their composition. The effect of the stabilizer on the structure of the Ag13 silver cluster was revealed in four model systems: gelatin, ammonium chloride NH4Cl, sodium borohydride NaBH4, and trisodium citrate Na3C6H5O (Na3Cit). Silver nanoparticles (AgNPs) obtained by the sonoelectrochemical, citrate, borohydride, and citrate-borohydride method varied in size from nanometers to several tens of nanometers. As a result of tribotechnical tests of lubricants with the obtained silver nanoparticles, a positive effect of stabilized silver clusters was revealed in the composition of lubricant compositions. The best tribotechnical characteristics were shown by lubricating compositions containing AgNPs stabilized with gelatin. It was found that a decrease in the size of gelatin stabilized AgNPs, when added to lubricants, leads to an increase in the tribological properties.

Freezing and Thawing Cycle Affecting Silver Nanocluster Formation on Polypropylene and Polyester Surface

Freezing and Thawing Cycle Affecting Silver Nanocluster Formation on Polypropylene and Polyester Surface

Combined Experimental and Theoretical Investigation on Formation of Size-Controlled Silver Nanoclusters under Gas Phase

Metallic nanoclusters (NCs) have been predicted to achieve the best Surface-Enhanced Raman Scattering (SERS) due to the controllable amount of atoms and structures in NCs. The Local Surface Plasmon Resonance (LSPR) effect on silver metal NCs (Ag) enables it to be a promising candidate for manipulating the LSPR peak by controlling the size of NCs, which in turn demands a full understanding of the formation mechanism of Ag. Here, we apply an extended Smoluchowski rate equation coupled with a fragmentation scheme to investigate the growth of size-selected silver NCs generated via a modulated pulsed power magnetron sputtering (MPP-MSP). A temperature-dependent fragmentation coefficient D is proposed and integrated into the rate equations. The consistency between the computational and experimental results shows that in relative low peak power ( W), the recombination of cation and anion species are the dominant mechanism for NC growth. However, in the higher region (≥800 W), the fragmentation mechanism becomes more impactful, leading to the formation of smaller NCs. The scanning electron microscopy observation shows the Ag is successfully soft-landed and immobilized on a strontium titanate crystal, which facilitates the application of the Ag/STO to the SERS research.

Detection of HIV/HCV virus DNA with homogeneous DNA machine-triggered in situ formation of silver nanoclusters

Currently, the early disease screening is still the most effective way to increase the survival rate of the HIV/HCV infected patients. However, the trace analysis remains a great challenge for early disease screening. Herein, a novel silver nanocluster (AgNCs) is in situ generated and served as fluorescence probes for the ultrasensitive HIV/HCV DNA detection by combing Exo III-assisted target recycling amplification (ERA) with rolling circle amplification (RCA). As an important key element of this sensor, the padlock probes (PLP) of RCA are exquisitely designed to compose of a guanine-rich (G-rich) region. Target DNA firstly hybridizes with the stem segment of the hairpin DNA (hp-DNA) and triggered the Exo III digestion, which releases and recycles the target and generate numerous ssDNA fragments. The generated ssDNA fragments act as ligation probes, which hybridize with PLP to trigger the RCA process, generating numerous periodically repeated cytosine-rich (C-rich) units. In the presence of NaBH4 and AgNO3, numerous AgNCs are in situ generated, thereby producing a strong fluorescent signal. Under optimal conditions, an ultrasensitive DNA machine is constructed for the detection of HIV DNA with a detection limit of 1.4 fM and a linear range of 10 fM to 100 pM. More fascinatingly, this DNA machine could intelligently distinguish multiple virus DNAs by the construction of analog AND and OR logic circuits.

A Computational Study on Reduction Mechanism of Silver Nanoparticles Synthesis

Abstract The redox reaction pathway of silver nanocluster formation in the polyol method is investigated by density functional theory calculation. It is suggested that the formation of Ag2(0) cluster with silver acetate dimer and glycol is more likely to occur via the Ag–carbon bond intermediate rather than via concerted double proton transfer or Ag-alkoxide intermediate. The aldehyde produced from glycol acts as a stronger reducing agent in the reaction. This mechanism provides important insights for controlling the reaction of the polyol process.

Formation of luminescent nanoclusters by etching silver nanoparticles with biomolecules

Metal nanoparticles and nanoclusters are progressively studied for use in various biomedical applications such as imaging, drug delivery, and therapies. Therefore, considering the interaction of biopolymers with metal nanostructures becomes vital for their efficient application. Luminescent metal nanoclusters are now widely considered as potential sensor applications. In this work we considered the interaction of silver nanoparticles with some proteins and oligonucleotides. We observed that biomolecules in some cases can effectively dissolve nanoparticles and lead to the formation of silver nanoclusters.

Thermally formation and luminescent performance of silver nanoclusters confined within LTA zeolites

In this research, the Linde Type A (LTA) zeolites were firstly synthesized with hydrothermal method and then the Ag+ ions were introduced into LTA through Ag+-Na+ exchange process, and the luminescent Ag3n+ nanoclusters can be formed inside the sodalite cages under heat treatment at 300–700 °C, which exhibited yellow-greenish emission under UV excitation. The XRD, SEM and TEM measurements were carried out to study the influence of Ag+ loading and heat treatment on the structure of LTA zeolite. The spectral measurement indicated the optimized Ag+-exchange level and heat treatment temperature, and the redshift of emission peak with increasing Ag+-loading or heat treatment temperature can be attributed to the interaction between Ag3n+ nanoclusters. When exposing in air, the emission intensity of Ag3n+ nanocluster was two orders of magnitude decreased while the re-heating can partially recover its emission. According to the XPS measurement and the AP calculation, this reduction in emission intensity can be assigned to the oxidation of silver atoms that constitute Ag3n+ nanoclusters.

Formation and Structure of Fluorescent Silver Nanoclusters at Interfacial Binding Sites Facilitating Oligomerization of DNA Hairpins.

Fluorescent, DNA-stabilized silver nanoclusters (DNA-AgNCs) are applied in a range of applications within nanoscience and nanotechnology. However, their diverse optical properties, mechanism of formation, and aspects of their composition remain unexplored, making the rational design of nanocluster probes challenging. Herein, a synthetic procedure is described for obtaining a high yield of emissive DNA-AgNCs with a C-loop hairpin DNA sequence, with subsequent purification by size-exclusion chromatography (SEC). Through a combination of optical spectroscopy, gel electrophoresis, inductively coupled plasma mass spectrometry (ICP-MS), and small-angle X-ray scattering (SAXS) in conjunction with the systematic study of various DNA sequences, the low-resolution structure and mechanism of the formation of AgNCs were investigated. Data indicate that fluorescent DNA-AgNCs self-assemble by a head-to-head binding of two DNA hairpins, bridged by a silver nanocluster, resulting in the modelling of a dimeric structure harboring an Ag12 cluster.

Formation and Structure of Fluorescent Silver Nanoclusters at Interfacial Binding Sites Facilitating Oligomerization of DNA Hairpins

AbstractFluorescent, DNA‐stabilized silver nanoclusters (DNA‐AgNCs) are applied in a range of applications within nanoscience and nanotechnology. However, their diverse optical properties, mechanism of formation, and aspects of their composition remain unexplored, making the rational design of nanocluster probes challenging. Herein, a synthetic procedure is described for obtaining a high yield of emissive DNA‐AgNCs with a C‐loop hairpin DNA sequence, with subsequent purification by size‐exclusion chromatography (SEC). Through a combination of optical spectroscopy, gel electrophoresis, inductively coupled plasma mass spectrometry (ICP‐MS), and small‐angle X‐ray scattering (SAXS) in conjunction with the systematic study of various DNA sequences, the low‐resolution structure and mechanism of the formation of AgNCs were investigated. Data indicate that fluorescent DNA‐AgNCs self‐assemble by a head‐to‐head binding of two DNA hairpins, bridged by a silver nanocluster, resulting in the modelling of a dimeric structure harboring an Ag12 cluster.

Oxometalate and phosphine ligand co-protected silver nanoclusters: Ag28(dppb)6(MO4)4 and Ag32(dppb)12(MO4)4(NO3)4.

Thiols, alkynyls and phosphines are the most widely used organic ligands to attain atomically precise metal nanoclusters, while oxometalates as inorganic ligands have almost been neglected in this field. Here, we used oxometalates (e.g., MoO42- and WO42-) as protecting ligands along with phosphines, such as 1,4-bis(diphenylphosphino)butane (dppb), to design and synthesize a new class of silver nanoclusters including Ag28(dppb)6(MoO4)4, Ag28(dppb)6(WO4)4 and Ag32(dppb)12(MoO4)4(NO3)4. Each cluster consists of a two-shell Ag4@Ag24 core protected by 4 oxometalates. These clusters exhibit similar optical absorption and photoluminescence properties that are not dependent on surface ligands. Furthermore, the electronic structure analysis shows that the clusters are 20-electron "superatoms". This work demonstrates that oxometalates can play a key role in the formation of silver nanoclusters, and the effect of oxometalates should be considered in the design and synthesis of metal nanoclusters.

Deciphering the Electroluminescence Behavior of Silver(I)‐Complexes in Light‐Emitting Electrochemical Cells: Limitations and Solutions toward Highly Stable Devices

AbstractIonic transition‐metal complexes based on silver(I) metal core (Ag‐iTMCs) represent an appealing alternative to other iTMCs in solid‐state lighting owing to (i) their low cost and well‐known synthesis, (ii) the tunable bandgap, and (iii) the highly efficient photoluminescence. However, their electroluminescence behavior is barely studied. Herein, the archetypal green‐emitting Ag‐iTMCs, namely [Ag(4,4′‐dimethoxy‐2,2′‐bipyridine)(Xantphos)]X (X = BF4, PF6, and ClO4), are thoughtfully investigated, revealing their electroluminescent features in light‐emitting electrochemical cells (LECs). Despite optimizing device fabrication and operation, luminance of 40 cd m−2, efficacy of 0.2 cd A−1, and a very poor stability of 30 s are achieved. This outcome encourages the comprehensive study of the degradation mechanism combining electrochemical impedance spectroscopy, X‐ray diffraction, and cyclic voltammetry techniques. These results point out the irreversible formation of silver nanoclusters under operation strongly limiting the device performance. As such, LECs are further optimized by (i) changing the counterions (PF6− and ClO4−) and (ii) decoupling electron injection and exciton formation using a double‐layered architecture. The synergy of both approaches leads to a broad exciplex‐like whitish electroluminescence emission (x/y CIE of 0.40/0.44 and color rendering index of 85) with an outstanding improved stability of ≈4 orders of magnitude (>80 h) without losing brightness (35 cd m−2).

Micropatterning of fluorescent silver nanoclusters in polymer films by Laser Interference

Hybrid films of poly (methacrylic acid) (PMAA) and silver fluorescent nanoclusters were structured by the Direct Laser Interference Patterning technique (DLIP) using few nanosecond laser pulses (355 nm) to obtain an arranged and well-defined periodic surface pattern. It is shown that the films of neat PMAA are not structured by irradiation at 355 nm due to its low absorbance at this wavelength. However, the silver nanoclusters act as chromophores increasing the absorbance of the film and allowing the surface patterning. Also, the interaction of the laser beam with a film of PMAA doped with Ag+ induces the formation of fluorescent silver nanoclusters and the subsequent surface patterning. The patterned films maintain the luminescent properties of the PMAA/Ag nanoclusters in solution. The structured and unstructured films were characterized by optical, atomic force and spectral laser confocal scanning microscopy showing highly oriented lines patterning already after just one laser pulse.

Experimental and theoretical study of the mechanism formation of silver nanoclusters in the reduction reaction of Ag+ ions by alizarin solution

For the study of the processes of the Ag+ ions interaction with humic substances a low molecular weight model compound – alizarin – was used for the first time in the present work. It has been established that alizarin carries out a double role in the process of synthesis of silver nanoparticles: reducing agent of Ag+ ions and a stabilizer of the formed nanoparticles. Based on the analysis of experimental data a mechanism of silver nanoparticles formation was proposed. In particular, at the moment of mixing of the reagents, a microphase Ag2O is formed and becomes a source of silver ions in solution. Alizarin molecules form a complex with silver ions, which provide the centres of primary clusters formation. The growth of primary clusters occurs through the reduction of Ag+ ions from the solution. Organic component of the complex undergoes oxidative hydroxylation by the Elbs reaction type.